The present invention relates to a natural circulation boiling water reactor and a handling method thereof.
The conventional natural circulation boiling water reactor is known in which a chimney is disposed above the core inside the reactor pressure vessel (see Japanese Patent Publication No. Hei 7-27051 for example). The chimney has a function for promoting natural circulation of the coolant in the reactor pressure vessel by introducing the coolant which is two-phase flow including gas and liquid and is exhausted from a core, to an upper portion in the reactor pressure vessel. This conventional chimney is formed of flow path partitions that are disposed in the reactor pressure vessel. FIG. 8a is a perspective view showing the conventional chimney and FIG. 8b shows cross section taken along a line Z-Z in FIG. 8a. As shown in FIG. 8a, the conventional chimney 211 forms flow paths 211a of the coolant by a plurality of division of the inside of the reactor pressure vessel (not shown), along the vertical direction thereof. As shown in FIG. 8b, the flow path partition walls 211b form grids in the cross sectional view and the flow paths 211a form a square shape. The flow path partition walls 211b are assembled as a grid of plate members of stainless steel for example and are integrally formed by welding at the position of intersection of each plate member